1. Field of the Invention
This invention relates to a novel liquid crystalline compound and a liquid crystal composition containing the same preferred for TFT.
2. Description of the Related Art
Nematic liquid crystal compositions have been broadly used as display materials for various display use applications such as watch, electronic calculator, word processor, computer terminal, television, etc. The modes for driving liquid crystal display elements using nematic liquid crystal compositions include mainly three kinds of twisted nematic mode (hereinafter abbreviated to TN), super-twisted nematic mode (hereinafter abbreviated to STN) and thin film transistor mode (hereinafter abbreviated to TFT). Among these, TFT mode is superior in the display capability, has been used for television or large type color display and enlargement of its use applications has been most expected.
As the characteristics required for liquid crystalline compounds for TFT, (1) exhibition of nematic liquid crystal phase within a broad temperature range, (2) a large dielectric anisotropy value (hereinafter abbreviated to .DELTA..epsilon.), (3) a large birefringence index (hereinafter abbreviated to .DELTA.n), (4) a low viscosity and (5) a chemical stability and a high voltage-holding ratio are mentioned. In order to satisfy these various characteristics, various compounds have been proposed.
As compounds having a high voltage-holding ratio, compounds containing fluorine atom are superior, and such liquid crystalline compounds have so far been vigorously searched. For example, a compound having 3,4-difluorobenzene core at the terminal of the molecule (DE 3042391) and further a compound having 3,4,5-trifluorobenzene core, aiming at a large .DELTA..epsilon. (U.S. Pat. No. 5,032,313)have been known, but these compounds have a very low clearing point; hence they are unsuitable.
Further, compounds having trifluoromethyl group, trifluoromethyloxy group or difluoromethyloxy group introduced at the terminal of the molecule (DE 4027840) have also been known, but they have had drawbacks of low clearing point and further a small .DELTA.n.
Further, in recent years, a compound having 1,1,2,2-tetrafluoroethyloxy group at the terminal of the molecule (DE 4142519) and a compound having 2,2,2-trifluoroethyloxy group at the terminal thereof (WO93/3113) have been reported, but either of these compounds have had drawbacks of a low clearing point and no sufficiently large .DELTA..epsilon. and .DELTA.n; hence they are insufficient in the characteristics. An example of a compound having introduced a cyano group having a larger dipole moment, aiming at exhibition of a larger .DELTA..epsilon. has been reported (Japanese patent application laid-open Nos. Sho 62-103057 and Sho 63-216858), but in these cases, the viscosity increases and the voltage-holding ratio lowers; hence it has been impossible to use them as liquid crystalline compounds for TFT.
Any of the above compounds disclosed in the prior art contain only a benzene ring and/or a cyclohexane ring, and there are almost no compounds containing a cyclohexene ring. The reason is considered as consisting in that compounds having a cyclohexene ring are liable to cause polymerization, decomposition, etc. due to various environment factors (moisture, heat, air, light, electricity, etc.) and hence are unstable (for example, U.S. Pat. No. 4,405,488).
As only a compound having a stable cyclohexene ring, there is a compound disclosed in Japanese patent application No. Hei 2-90190 (U.S. Pat. No. 5,064,565), but it does not exhibit a sufficiently large .DELTA..epsilon.; hence it has been unsuitable as a liquid crystal compound for TFT.
Further, EP 334911 claims a compound expressed by the formula containing a cyclohexene ring, but as to its concrete compound, there is no description suggesting an example or characteristics supporting it.
Problem to be Solved by the Present Invention
The object of the present invention is to provide a liquid crystalline compound which has overcome the above drawbacks of the prior art, exhibit a nematic liquid crystal phase within a broad temperature range and also has a large .DELTA..epsilon. and .DELTA.n and further has a high voltage-holding ratio, and a liquid crystal composition containing the same preferred for TFT.
Means for Solving the Problem
In order to achieve the above object, the inventions to be claimed are as follows:
(1) A liquid crystalline compound expressed by the formula (I) ##STR2## wherein R.sub.1 represents an alkyl group of 1 to 12 carbon atoms and one or two not adjacent CH.sub.2 groups excluding the terminal in the alkyl group may be replaced by oxygen atom, --CO-- group, --OCO-- group, --COO-- group or --CH.dbd.CH-- group; X and Z each represent H, F or Cl atom; Y represents a perfluoroalkyl group or a perfluoroalkyloxy group of 1 to 4 carbon atoms and one or two F atoms in these groups may be replaced by H atom; one of A, B and C each represent cyclohexene ring and the others thereof can be chosen from among covalent bond or cyclohexane ring and benzene rings and these rings may be substituted by F atom or Cl atom; and l, m and n each are 0 or 1 independently of each other, but when m=0, l=0. PA1 (2) A liquid crystalline compound according to item (1), wherein R.sub.1 represents an alkyl group or an alkyloxy group of 1 to 12 carbon atoms. PA1 (3) A liquid crystalline compound according to item (1), wherein Y represents trifluoromethyl group. PA1 (4) A liquid crystalline compound according to item (1), wherein Y represents trifluoromethyloxy group. PA1 (5) A liquid crystalline compound according to item (1), wherein Y represents difluoromethyloxy group. PA1 (6) A liquid crystalline compound according to item (1), wherein Y represents 1,1,2,2-tetrafluoroethyloxy group. PA1 (7) A liquid crystalline compound according to item (1), wherein Y represents 1,1,2,3,3,3-hexafluoropropyloxy group. PA1 (8) A liquid crystalline compound according to item (1), wherein Y represents pentafluoroethyloxy group. PA1 (9) A liquid crystal composition comprising two or more components at least one of which is a liquid crystalline compound set forth in either one of items (1) to (8). PA1 (10) A liquid crystal composition comprising as a first component, at least one compound set forth in either one of items (1) to (8) and as a second component, at least one compound chosen from among those of the following formulas (2), (3) and (4): ##STR3## wherein R.sub.2 represents an alkyl group of 1 to 10 carbon atoms; Z' represents F or Cl; Q.sub.1 and Q.sub.2 each represent H or F independently of each other; r represents 1 or 2; and Z.sub.1 and Z.sub.2 each represent --CH.sub.2 CH.sub.2 -- or covalent bond independently of each other. PA1 (11) A liquid crystal composition comprising as a first component, at least one compound set forth in either one of items (1) to (8), and as a second component, at least one compound chosen from among those of the following formulas (5), (6), (7), (8) and (9): ##STR4## wherein R.sub.3 represents an alkyl group of 1 to 10 carbon atoms or an alkenyl group of 2 to 10 carbon atoms and optional methylene group (--CH.sub.2 --) excluding the terminal in these groups may be replaced by oxygen atom (--O--), but two or more methylene groups should not be continuedly replaced by oxygen atom; Z.sub.3 represents --CH.sub.2 CH.sub.2 --, --COO-- or covalent bond; Q.sub.3 represents H or F; D represents cyclohexane ring, benzene ring or 1,3-dioxane ring; and s represents 0 or 1, ##STR5## wherein R.sub.4 represents an alkyl group of 1 to 10 carbon atoms, and optional methylene group (--CH.sub.2 --) excluding the terminal in the group may be replaced by oxygen atom (--O--), but two or more methylene groups should not be continuedly replaced by oxygen atom; Q.sub.4 represents H or F; and k represents 0 or 1, ##STR6## wherein R.sub.5 represents an alkyl group of 1 to 10 carbon atoms, and optional methylene group (--CH.sub.2 --) excluding the terminal in the group may be replaced by oxygen atom (--O--), but two or more methylene groups should not be continuedly replaced by oxygen atom; E represents cyclohexane ring or benzene ring; Q.sub.5 represents H or F; Z.sub.4 represents --COO-- or covalent bond; and h represents 0 or 1, ##STR7## wherein R.sub.6 and R.sub.7 each represent an alkyl group, an alkyloxy group or an alkyloxymethyl group of 1 to 10 carbon atoms, independently of each other, and optional methylene groups (--CH.sub.2 --) excluding the terminal in these groups may be replaced by oxygen atom, but two or more methylene groups should not be continuedly replaced by two or more oxygen atoms; L represents cyclohexane ring, pyrimidine ring or benzene ring; G represents cyclohexane ring or benzene ring; and Z.sub.5 represents --C.tbd.C--, --COO--, --CH.sub.2 CH.sub.2 -- or covalent bond, ##STR8## wherein R.sub.8 represents an alkyl group or an alkyloxy group of 1 to 10 carbon atoms; R.sub.9 represents an alkyl group, an alkyloxy group or an alkyloxymethyl group of 1 to 10 carbon atoms, and optional methylene group (--CH.sub.2 --) excluding the terminal in these groups may be replaced by oxygen atom (--O--), but two or more methylene groups should not be continuedly replaced by oxygen atom; M represents cyclohexane ring or pyrimidine ring; J and K each represent cyclohexane ring or benzene ring independently of each other; Z.sub.6 represents --COO--, --CH.sub.2 CH.sub.2 -- or covalent bond; Z.sub.7 represents --C.tbd.C--, --COO-- or covalent bond; and Q.sub.6 represents H or F. PA1 (12) A liquid crystal display element composed using a liquid crystal composition comprising two or more components, at least one of which contains at least one liquid crystalline compound recited in either one of items (1) to (8). PA1 (13) A liquid crystal display element composed using a liquid crystal composition comprising two or more components, at least one of which contains at least one liquid crystalline compound recited in either one of items (9) to (11). PA1 --CF.sub.3 --OCF.sub.3 PA1 --CF.sub.2 H --OCF.sub.2 H PA1 CF.sub.2 CF.sub.2 H --OCF.sub.2 CF.sub.2 H PA1 CF.sub.2 CF.sub.3 --OCF.sub.2 CF.sub.3 PA1 CF.sub.2 CFHCF.sub.3 --OCF.sub.2 CFHCF.sub.3
Any of the liquid crystalline compounds expressed by the formula (I) have superior liquid crystal characteristics, and liquid crystalline compounds having particularly superior characteristics among the above, that is, those which exhibit nematic liquid crystal phase within a broad temperature range, have a large .DELTA..epsilon. and .DELTA.n and a low viscosity and have a high voltage-holding ratio are (1--1) to (1-25) mentioned below: ##STR9##
In these formulas, R.sub.1, X, Y and Z each are as defined above, and T.sub.1, T.sub.2, T.sub.3 and T.sub.4 each represent F or Cl atom independently of each other.
Among the above, those wherein the substituent Y is chosen from among the followings exhibit particularly preferable characteristics:
Although any of the compounds expressed by the formula (I) of the present invention can be a component constituting liquid crystal compositions having superior characteristics, tricyclic compounds or tetracyclic compounds are preferably chosen and used in the case where a liquid crystal composition having a particularly high clearing point is required, whereas bicyclic compounds are preferably chosen and used in the case where a liquid crystal composition having a somewhat low clearing point is required. Although any of the compounds of the present invention expressed by the formula (1) exhibit a large .DELTA..epsilon., at least one of X, Z, T.sub.1, T.sub.2, T.sub.3 and T.sub.4 is preferred to be F or Cl atom, in the case where a particularly large .DELTA..epsilon. is required, and a compound containing a number of benzene rings is preferred in the case where a large .DELTA.n is required. The compounds of the present invention do not contain any cyano group or the like as substituent example raising the viscosity; hence any of them have a low viscosity, but in the case where a lower viscosity is required, a compound containing a number of cyclohexane rings is preferred. As described above, according to the present invention, when X, Z, T.sub.1, T.sub.2, T.sub.3 and T.sub.4 as well as the ring core are suitably chosen, it is possible to optionally obtain compounds having necessary values of physical properties.
The compounds of the present invention are prepared by subjecting an alcohol substance obtained by reacting various Grignard reagents with cyclohexanone derivatives, to dehydration reaction. ##STR10##
Namely, a compound (1a) of the formula (1) wherein B represents a cyclohexene ring can be prepared by reacting a Grignard reagent prepared from a 2--substituted ethyl halide (11), with a cyclohexanone derivative (10) to obtain an alcohol substance (12), followed by dehydrating it. In addition, in the preparation of the above (12) the Grignard reagent may be replaced by a 2-substituted ethyllithium. The above dehydration reaction easily proceeds in the presence of an acidic catalyst. As the acidic catalyst used, mineral acids such as sulfuric acid, hydrochloric acid, etc., sulfonic acids such as p-toluenesulfonic acid or their salts, and acidic ion exchange resins such as Amberlyst, etc. are broadly suitable. Further, compound (1a) can be prepared without isolating (12), by once converting the tertiary hydroxyl group of (12) into a leaving groups such as mesyl group, tosyl group, halogens, etc., followed by treatment with bases such as NaOH, NaH, DBU, etc., or by reacting a Grignard reagent prepared from (11), with (10), followed by bringing the reaction system into an acidic condition.
The starting raw material (10) can be obtained by reacting compound (13) with commercially available 1,4-cyclohexanedione monoethylene ketal (14) to obtain (15), followed by subjecting it to dehydration, reduction, and removal of protective group. The dehydration reaction can be carried out in the same manner as the above. Further, the reduction reaction can be carried out in a hydrogen atmosphere in the presence of a catalyst such as Pd-C, Pt-C, Raney Ni, etc. Further, the reaction of removal of protective group can be easily carried out by heating (17) under an acidic condition, preferably in formic acid. (11) used for preparing the Grignard reagent is prepared by halogenating an alcoholic substance (19) obtained by subjecting compound (18) to carbon-number-increasing reaction, with various halogenating agents. As the halogenating agents, hydrogen bromide, hydrobromic acid, phosphorus tribromide, thionyl chloride, etc. are preferably mentioned. The carbon number-increasing reaction may be carried out according to a known process of effecting the reaction, but a process of using ethylene oxide is most simple and preferable.
Next, compound (1b) of the formula (1) wherein C represents cyclohexene ring can be prepared by reacting a Grignard reagent prepared from 2-substituted ethylhalide (20), with cyclohexanone derivative (21), to obtain an alcoholic substance (22), followed by dehydrating it. ##STR11##
In addition, in the preparation of the above (22), the Grignard reagent can be replaced by 2-substituted ethyllithium. The above dehydration reaction may be carried out as above. The starting raw material (21) can be obtained by reacting commercially available 1,4-cyclohexanedione monoethylene ketal (14) with a phenylmagnesium halide (23) to obtain (24), followed by subjecting it to dehydration, reduction and protective group-removing reaction as in the case of preparation of the above (10).
In addition, in any of the above preparation processes, if the Y in the formula contains hydrogen atom, the reactivity of this hydrogen is very high; hence these preparation processes cannot be applied. Thus, in such a case, the following process is suitable: ##STR12##
Namely, a compound (27) wherein Y represents benzyl ether is obtained in advance, followed by removing the benzyl ether to obtain a compound (28) having a hydroxyl group, and introducing a fluoroalkyl group into the phenolic hydroxyl group, to obtain a compound of the formula (1c). In this case, it does not matter if a protective group other than benzyl ether, for example, silyl ethers such as trimethylsilyl ether, acetals such as methoxymethyl ether is used, etc. is used. Introduction of a fluoroalkyl group into (28) can be carried out by reacting various fluorine-containing compounds under basic condition.
Any of the thus obtained compounds (1) of the present invention exhibit a large .DELTA..epsilon. and .DELTA.n, and are chemically stable in spite of containing cyclohexene ring; hence they have a high voltage-holding ratio and further are easily miscible with various liquid crystal compounds; thus they are far superior as a component of nematic liquid crystal compositions, particularly of nematic liquid crystal compositions suitable to electro-optical elements.
The liquid crystal composition provided by the present invention may be composed only of component (A) containing at least one compound expressed by the formula (1), but a mixture of the above component (A), with as a second component, at least one compound chosen from the groups consisting of the above formulas (2), (3) and (4), and/or at least one compound chosen from the groups consisting of the above formulas (5), (6), (7), (8) and (9) is preferable, and further, in accordance with the objects, compounds optionally chosen from compounds of the groups (B) having .DELTA..epsilon..gtoreq.5, those of the group (C) having .vertline..DELTA..epsilon..vertline.&lt;5, those of the group (D) having a clearing point of particularly 80.degree. C. or higher, and those of the group (E) other than the above, can be mixed.
Among the above second components, as preferable examples of compounds included in the formula (2), the following (2-1) to (2-12) can be mentioned: ##STR13##
Among the second component, as preferable examples of compounds included in the formula (3), the following (3-1) to (3-18) are, mentioned: ##STR14##
Among the second component, as preferable examples of compounds included in the formula (4), the following (4-1) to (4-18) are mentioned: ##STR15##
These compounds expressed by the formulas (2) to (4) are those having a positive dielectric anisotropy and have a far superior thermal stability and chemical stability. Thus, the compounds are indispensable in the case where a liquid crystal composition for TFT (AM-LCD), for which particularly a high voltage-holding ratio and a larger specific resistance value with a high reliability are required.
The quantity of the compounds used is suitably within a range of 1 to 99% by weight based upon the total weight of the liquid crystal composition in the case where a liquid crystal composition for TFT is prepared, and preferably 10 to 97% by weight, more preferably 40 to 95% by weight. Further, at that time, the compound expressed by the formulas (5) to (9) may be partly contained. In addition, in the case where a liquid crystal composition for STN display mode or usual TN display mode is prepared, too, it is possible to use compounds expressed by the formulas (2) to (4).
Next, among the above second component, as preferable examples of compounds included in the formula (5), the following (5-1) to (5-17) are mentioned: ##STR16##
Among the second component, as preferable examples of compounds included in the formula (6), the following (6-1) to (6-3) are mentioned. ##STR17##
Among the second component, as preferable examples of compounds included in the formula (7), the following (7-1) to (7-9) are mentioned: ##STR18##
Compounds expressed by the formulas (5) to (7) have a positive and large dielectric anisotropy value; hence they can be used particularly for reducing the threshold voltage of the liquid crystal composition. Further, they can be also used for adjusting the viscosity and .DELTA.n, and besides for broadening the nematic temperature range by raising the clearing point or by other means, and further for improving the steepness.
Among the second component, as preferable examples of compounds included in the formula (8), the following (8-1) to (8-6) can be mentioned: ##STR19##
Further, among the second component, as preferable examples of compounds included in the following (9-1) to (9-10) can be mentioned: ##STR20##
Compounds expressed by the formulas (8) and (9) are those having a negative or weak, positive dielectric anisotropy. Among them, compound of the formula (8) can be used mainly for the viscosity reduction and/or .DELTA.n adjustment of liquid crystal composition. Further, compound of the formula (9) can be used for broadening the nematic temperature range by raising the clearing point or by other means and/or for adjusting the .DELTA.n.
Among the second component, compounds expressed by the above formulas (5) to (9) are indispensable particularly for preparing liquid crystal compositions for STN display mode or usual TN display mode.
In this case, the quantity of the compounds used is suitably within a range of 1 to 99% by weight based upon the total weight of the liquid crystal composition, preferably 10 to 97% by weight, more preferably 40 to 95% by weight.
Further, at that time, compounds expressed by the formulas (2) to (4) may be partly used.
Next, (B), (C), (D) and/or (E) are added to the liquid crystal composition in accordance with the object, and examples of compounds included therein are as follows:
Firstly, as preferable examples of compounds included in (B), the following (B1) to (B13) can be mentioned: ##STR21##
(In the above compounds, Ra represents an alkyl group or an alkenyl group of 1 to 10 carbon atoms, but one or two or more not adjacent carbon atoms therein may be replaced by oxygen atom.)
Further, as preferable examples of compounds included in (C), the following (C1) to (C34) can be mentioned: ##STR22##
(In the above compounds, Ra and Ra' each represent an alkyl group or an alkenyl group of 1 to 10 carbon atoms, and one or two or more not adjacent carbon atoms therein may be replaced by oxygen atom.)
Further, as preferable examples of compounds included in (D), the following (D1) to (D57) can be mentioned: ##STR23##
Further, as preferable examples of compounds included in (E), the following (E1) to (E18) can be mentioned: ##STR24##
As to the liquid crystal compositions of the present invention, it is preferred to contain one or more compounds expressed by the formula (1) in a proportion of 0.1 to 99% by weight, in order to exhibit superior characteristics.
When the liquid crystal compositions are used for TFT liquid crystal display elements, it is possible to improve steepness and viewing angle. Further, since the compound of the formula (1) is a low viscosity compound, the response speed of liquid crystal display elements using the compound is improved.
The liquid crystal composition of the present invention is prepared generally according to known process, for example, a process of mixing various components at a high temperature and dissolving in each other. Further, if necessary, a suitable additive is added, whereby improvement is carried out in accordance with aimed use applications, to optimize the compositions. Such additives have been well known by person of ordinary skill in the art, and have been described in literatures or the like in detail. Usually, a chiral dopant inducing the helical structure of liquid crystals to thereby adjust necessary twisted angle and prevent reverse twist.
As examples of the liquid crystal compositions containing the compound of the present invention, the following can be mentioned, and in addition, the compound Nos. are the same as those shown in the following Examples: ##STR25##